.\" -*- nroff -*-
.\" Copyright 2013-2015 Los Alamos National Security, LLC. All rights reserved.
.\" Copyright 2010 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" $COPYRIGHT$
.TH MPI_Compare_and_swap 3 "Jun 10, 2020" "4.0.4" "Open MPI"
.SH NAME
\fBMPI_Compare_and_swap\fP \- Perform RMA compare-and-swap

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Compare_and_swap(const void *\fIorigin_addr\fP, const void *\fIcompare_addr\fP,
	void *\fIresult_addr\fP, MPI_Datatype \fIdatatype\fP, int \fItarget_rank\fP,
	MPI_Aint \fItarget_disp\fP, MPI_Win \fIwin\fP)

.fi
.SH INPUT PARAMETERS
.ft R
.TP 1i
origin_addr
Initial address of buffer (choice).
.ft R
.TP
compare_addr
Initial address of compare buffer (choice).
.ft R
.TP
result_addr
Initial address of result buffer (choice).
.ft R
.TP
datatype
Data type of the entry in origin, result, and target buffers (handle).
.ft R
.TP 1i
target_rank
Rank of target (nonnegative integer).
.ft R
.TP 1i
target_disp
Displacement from start of window to beginning of target buffer (nonnegative integer).
.ft R
.TP 1i
win
Window object (handle).

.SH OUTPUT PARAMETER
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
This function compares one element of type \fIdatatype\fP in the compare buffer \fIcompare_addr\fP with the buffer at offset \fItarget_disp\fP in the target window specified by \fItarget_rank\fP and \fIwin\fP and replaces the value at the target with the value in the origin buffer \fIorigin_addr\fP if the compare buffer and the target buffer are identical. The original value at the target is returned in the buffer \fIresult_addr\fP. The parameter \fIdatatype\fP must belong to one of the following categories of predefined datatypes: C integer, Fortran integer, Logical, Multi-language types, or Byte as specified in MPI-3 § 5.9.2 on page 176.
.sp
The origin and result buffers (\fIorigin_addr\fP and \fIresult_addr\fP) must be disjoint.

.SH FORTRAN 77 NOTES
.ft R
The MPI standard prescribes portable Fortran syntax for
the \fITARGET_DISP\fP argument only for Fortran 90.  FORTRAN 77
users may use the non-portable syntax
.sp
.nf
     INTEGER*MPI_ADDRESS_KIND \fITARGET_DISP\fP
.fi
.sp
where MPI_ADDRESS_KIND is a constant defined in mpif.h
and gives the length of the declared integer in bytes.

.SH NOTES
It is the user's responsibility to guarantee that, when
using the accumulate functions, the target displacement argument is such
that accesses to the window are properly aligned according to the data
type arguments in the call to the \fBMPI_Compare_and_swap\fP function.

.SH ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument.
.sp
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler
may be changed with \fBMPI_Comm_set_errhandler\fP; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.
